Slow setting cement



Patented Mar. 4, 1941 A UNITED," STATES PATENT OFFICE SLOW SETTING CEMENT Thomas H. Dunn, Tulsa, Okla, assignor to Stanolind Oil & Gas Company, Tulsa, Okla., a corporation of Delaware No Drawing. Application June 22, 1939,

Serial No. 280,585

a 12 Claims. (01. 106--24) This invention relates to slow setting cements pressure conditions encountered in oil and gas and a method of making them and more particuwells. Other and more detailed objects, advanv larly to slow setting cements used in cementing tages, and uses of my invention will become operations in oil and gas well work. apparent'as the description thereof proceeds.

Large quantities of cementare used in oil wells Various slow setting cements have been used in cementing casing to exclude water, in cement and proposed in which a number of different squeeze jobs, and in other phases of oil field pracmaterials have been used to delay the setting tice well known to those familiar with the art. time. Amongst such materials are the ordinary Cement is placed at the desired point in various. phosphates, i. e. the normal and acid orthoways such as pumping the cement through the phosphates. 10 casing or tubing, lowering the cement into the I have found that results far superior to those hole by means of a dump bailer or other methods. obtainable with the ordinary phosphates hereto- It is essential that the cement does not set before fore used, can be obtained by the use of very it is placed in the desired position and it is desirsmall quantities of certain metaphosphates,

able that the cement be as fluid as the particular namely the polymerized metaphosphates, in small 15 job permits. For deep well cementing ordinary quantities in cements. oil well cement is unsuitable largely because of Thus for instance in one particular lot of the decreased setting time of the cement due Portland cement the addition of 0.10% of sodium to relatively high subsurface temperatures and hexametaphosphate increased the initial setting pressures. In many instances before ordinary time, as determined by the use of the Vicat needle 20 cement can be placed in position, a stiffening or tester, from 4 hours-and 45 minutes to 17 hours gelling of the-slurry occurs which requires abnorand 55 minutes. Similarly the final setting time mal pump pressures to complete the job. ,as determined with the Vicat tester was in- In addition to rendering a cement diflicult to creased from 6 hours and 20 minutes, without 5 pump and decreasing the time required for the addition of a retarder, to 19 hours and 40 gellation to occur within the cement slurry, deteminutes, in the presence of 0.10% of sodium rioration of the cement itself results when the hexametaphosphate. cement is agitated during this stiflening or gelling The vastly superior results obtainable by the period. use of sodium hexametaphosphate as compared In plug back and squeeze cementing where the with various other phosphates is shown by the 30 slurry is required to be forced out into the waterfollowing table: 0 bearing formations, the cement comes to rest, or nearly so, under high temperature conditions.

Also a considerable length of drill pipe or tubing ohemicval Weight 3%? o :2 must be worked into a body of cement in the hole. initial mm] 5 The first danger is that the slurry will gel, thus making a satisfactory job impossible. The second Hrs Hrs Min daggler is that (g isctliciting the pipe. tiA 1cement 303 111 heindametapllliosplhiagaun 3 13 g is 235 w e rema ns u or a; compara ve y long Pym! 40 period removes the hazard and improves the i di g figzwfigfg f f fl 31:8 13 g 55 40 results of this type f j b V Disodlum phosphate. 0.10 2 2 15 I The fore oing is not intended to cover all Phases cementing but is mentmned Moreover these results obtainable with sodium show the desirability of retarding the setting hemmebaphosphate and ther olymerized t 45 time Of ordinary Portland cement as well aS' phosphates cannot be duplicated by the use of 45 decrease the and gel strength n even larger quantities of various of the other cement mphosphates.- Thus for example the use of 0.20% i It is an object of this invention to overcome of sodium acid pyrophosphate increased the inithe dlfllculties above mentioned. Another object ha] setting time only 4 hours, while the use of of this invention is to produce new and improved 114.0% .of t t sodium pyrophbsphate gave 50 slow setting cements. A further object 01 this retardation of only 8 hours and 35 minutes. inventionis to provide new methods of making Sodium hexametaphosphate can be made in slow setting cements. A still further object of various ways and is an article of commerce. It this invention'is to provide slow setting cements is believed to have the formula NadPOslu but 65 having improved properties for use under high various other forms include NaazNa POa a and Na4:Naa(POa)e may be present and are also known as sodium hexametaphosphate.

Moreover other alkali metal metaphosphates,

similar to the other alkali metal compounds l mentioned. Also the corresponding mixed salts can be used, for instance flve of the sodium atoms of sodium hexametaphosphate can be replaced with ammonium to form a substance with the empirical composition (NH4) 5Na(POa) e. The

corresponding acid salts can also be used and are included within the expression alkali metal metaphospha Further, while I prefer to use an alkali metal 1 hexametaphosphate, more particularly sodiumhexametaphosphate, other metaphosphates which maybe defined as salts of (HPOaln in which n is an integer having a value of at least two, can be used. In other words the alkali metal salts of metaphosphoric acid polymers are preferred.

' 'Another example of a desirable compound for use *in my invention is sodium tetrametaphosphate; which is vbelieved to have the formula NadPOa) 4. In the case of these other metaphos- I "phates and as in thecase oi the hexametaphosphates,-the various alkali metal salts (including ammonium compounds, the mixed salts, and the acid salts) can beused. V a The amount of alkali metal metaphosphate used varies with .the'particular cement, the par- I ticular-metaphosphate chosen and the desired hours. The average results are given in the 101- lowing table:

mam set mm m at70 F. at 70 F.

Min. HraMi'n. Avcrageiormitreated cement 5 44 7 18 Average for treated cement.-. 10 33 18 36 It will be apparent that these retardations make possible the use of my new treated cements .60 under field conditions where ordinary cements, or even cements with prior art retarders, would cause great dimculty, due to rapid setting. .Thus, for instance, ii-the setting time is low, an enormous amount oi. cement must be gotten into the 05 well in a very short time, with the result that a large crew of men must be used, with consequent increased expense. Moreover, cements with prlor art retarders which show reasonably satisfactory properties .7 when tested at atmospheric pressure, appear to disintegrate in the well and give complete unsatisfactory results under the temperature and pressure conditions encountered in oil and gas. wells, while cements with my retarders, function under the high temperatures and pressures encountered in well operations in the same manner 5 as at atmospheric temperature and pressure.

Another striking advantage of my cements is that-the tensile strength is not substantially reduced by the use of my retarders while most other retarders cause marked reductions in tensile strength. Thus the use of 0.10% 01 sodium hexametaphosphate reduced the 14 day tensile strength of one cement by only 5% while the use of 0.05% of this compound actually increased the '1 day tensile strength oi. another cement by 3%. 15

' I prefer to use these retarders in Portland cement but they can be used in other cements as well.

Instead of mixing the dry retarder with the dry cement the retarder can be added to the 20 water used in making the slurry or otherwise incorporated in the cement or concrete.

I claim: h

1. A method of. retarding the setting time of cement comprising adding an alkali metal hexa- 25 metaphosphate thereto.

2. A method or retarding the setting time of a cement comprising adding thereto a small but effective amount of sodium hexametaphosphate.

3. A method of retarding the setting time of a 30 Portland cement comprising introducing into said cement from about 0.01% to about 1.00% of an 'alkali metal salt of a metaphosphoric acid phate..

5. A method of cementing a well comprising" introducing into said well, a Portland cement l0- slurry-carrying a quantity of an an alkali metal salt of a metaphos'phoric acid polymer equal to from 0.01% to about 1.00% of the Portland cement present in said slurry.

6. A method of cementing a well comprising 45 introducing into said well a cement slurry carrying a minor quantity of sodium hexametaphosphate. r

7. A slow setting Portland cement comprising from about 0.01% to about 1.00% oian alkali metal salt of a metaphosphoric acid polymer.

8. A slow setting cement comprising a small amount of an alkali metal hexametaphosphate.

9. A Portland cement for use under high pressures comprising from about 0.01% to about 55 1.00% .0! .an alkali metal salt of a polymer of metaphosphoric acid.

10. A cement for use under high pressures comprising from about 0.03% to about 0.30% of an alkali metal hexametaphosphate. do

11. A Portland cement slurry comprising an amount of an alkali metal salt of a metaphosphoric acid polymer equalto from about 0.01% to about 1.00% of the Portland cement present in said slurry. 05

12. A cement slurry comprising an amount of analkali metal hexametaphosphate equal to from "about 0.01% to about 1.00% of the weight of the cement. i

moms n. norm.

" CERTIFICATE OF CORRECTION.

Patent No. 2,255,975. Y March L;,-19h1. THOMAS 11. DUNN.

It is hereby certified that error appears in the printed specification ofthe abo ve numbered patent requiring correction as follows: Page 2, second column, line L l, claim 5, for "an en" read -an--; line 1;.5,'same claim,

after the word "from" insert --abo1 1t'-; and that the said Letters Patent.

I shou ld be read with this correction therein that the same may conform to the record of the case in the Patent Office;

Signed and sealed this 1st day of April, A. D. 19141.

.5 Henry Van Arsdale,

(Seal) Acting-Commissioner of Patents. 

